Damping means for increasing the minimum dynamic stiffness of a shaft

ABSTRACT

The minimum dynamic stiffness of a spindle of a grinding wheel is increased by having a sleeve of viscoelastic material bonded to the spindle between the bearing supports for the spindle. A sleeve surrounds the viscoelastic material sleeve to constrain the sleeve of viscoelastic material to increase its shear strains and is bonded thereto.

United States Patent Hasz [451 Sept. 19, 1972 [54] DAMPING MEANS FORINCREASING THE MINIMUM DYNAMIC STIFFNESS OF A SHAFT.

[72] Inventor: John R. Hasz, 5686 Sherwood Drive, Milford, Ohio 45150[22] Filed: Sept. 23, 1971 [21] Appl. No.: 183,035

Related US. Application Data [62] Division of Ser. No. 857,155, Sept.11, 1969,

Pat. No. 3,664,228.

52 U.S.C1. ..308/l,51/l69,64/1V, 74/574, 188/1 B 51 int, Cl..B24b45/00,F16f15/00 [58] Field of Search ..51/168, 169, 166 R, 166 TS;74/574; 64/1 V; 308/1, 73; 188/1 B; 90/11 A, 11 R; 77/58 B; 82/D1G. 9

[56] References Cited UNITED STATES PATENTS Ray ..5 l69 X 1,697,046Chapman ..51/166 TS 2,001,167 5/1935 Swennes ..64/1 V 2,582,873 1/1952Larson ..51/166 TS 2,747,440 5/1956 Kyser ..77/58 B 3,292,237 12/1966Fisher ..77/58 B 3,385,009 5/1968 Lueders ..51/ 168 3,463,048 8/1969Owsen ..90/11 A Primary Examiner-Donald G. Kelly Attorney-Frank C.Leach, Jr.

[57] ABSTRACT The minimum dynamic stiffness of a spindle of a grindingwheel is increased by having a sleeve of viscoelastic material bonded tothe spindle between the bearing supports for the spindle. A sleevesurrounds the viscoelastic material sleeve to constrain the sleeve ofviscoelastic material to increase its shear strains and is bondedthereto.

'12 Claims, 6 Drawing Figures P'A'TENTEB SEP 19 I972 SHEET 2 OF 2DAMPING MEANS FOR INCREASING THE MINIMUM DYNAMIC STIFFNESS OF A SHAFIThis application is a division of application Ser. No.

857,155, filed Sept. 11, 1969, now US. Pat. No. 3,664,228, issued May23, 1972.

In machine tools such as a grinding machine, for example, thedisplacement of the grinding wheel due to the force created byengagement with the workpiece being ground creates a bending of thegrinding wheel spindle between its support bearings. Thisbending of thespindle between its support bearings introduces a vibration in thespindle that is transmitted to the grinding wheel to produceregenerative chatter when the ratio of the cutting stiffness, which isthe spring constant between the cutting element and the material, to theminimum dynamic stiffness of the spindle exceeds one-half. The cuttingstiffness may be lowered by decreasing the feedrate of the grinding.wheel into the workpiece, reducing the width of the grinding wheel,dressing the grinding wheel more often, or increasing the surface speedof the grinding wheel.

Therefore, to insure that regenerative chatter does not occur, thecutting parameters of the grinding machine must be selected so that theratio of.the cutting stiffness to the minimum dynamic stiffness is equalto or less than one-half; this is known as the borderline of stability.Accordingly, this necessitates the grinding operation to be-performed atless than opminimum dynamic stiffness of the spindle will allow thecutting stiffness to be increased without the ratio of the cuttingstiffness to the dynamic stiffness exceeding onehalf wherebyregenerative chatter could occur. Thus, by increasing the minimumdynamic stiffness of the spindle, one or more of the grinding parameterscan be changed to lower the time period for grinding withoutregenerative chatter occurring. That is, the feedrate of the grindingwheel workpiece can be increased, the speed of rotation of the grindingwheel can be decreased, the width of the grinding wheel canbe increased,and the grinding wheel may be dressed at longer intervals. Any of theforegoing will decrease the period required for grinding a particularpart so that the unit cost for grinding workpieces can be substantiallyreduced when the minimum dynamic stiffness of the spindle is increased.

The present invention satisfactorily solves the foregoing problem byutilizing damping means to increase the minimum dynamic stiffness of thespindle, preferably to a maximum. As a result, the cutting stiffness canbe increased, and the ratio of the cutting stiffness to the minimumdynamic stiffness of the spindle still maintained equal to or less thanone-half. Accordingly, by utilizing the damping means of the presentinvention to increase the minimum dynamic stiffness of the spindle, theunit cost for grinding workpieces is substantially reduced in comparisonwith the unit cost for grinding workpieces on the same grinding tor.

machine without the damping means of the present invention.

The present invention utilizes a viscoelastic material to increase theminimum dynamic stiffness of the'spindie. The present invention does notrequire any tuning of the damping means as is required when tuned dampedvibration absorbers are used. It is only necessary to dispose theviscoelastic material so that it absorbs the vibrations of the spindle.The viscoelastic material absorbs energy from compression, tension, andshear strains created therein by the'bending of the spindle between itsbearing supports. Thus, the viscoelastic material of the presentinvention is an energy dissipa- An object of this invention is toprovide damping means to increase the minimum dynamic stiffness of ashaft.

Other objects of this invention will be readily perceived from thefollowing description, claims, and drawings. 7

This invention relates to the combination of a rotating shaft havinglongitudinally spaced portions supported by hearing means. Damping meansis disposed between the bearing means to increase the minimum dynamicstiffness of the rotating shaft with the damping means disposed in atleast partial surrounding relation to the rotating shaft to be movablein response to vibrations of the rotating shaft to absorb thevibrations. The damping means is mounted on the rotating shaft so as tonot be slidable relative thereto.

The attached drawings illustrate a preferred embodiment of theinvention, in which:

FIG. 1 is a front elevational view of a centerless grinding machine inwhich the damping means of the present invention may be employed;

FIG. 2 is a'longitudinal sectional view of the spindle of the grindingwheel having the damping means thereon with various other elements ofthe grinding machine shown in phantom and taken along line 2-2 of FIG.1;

FIG. 3 is a longitudinal sectional view illustrating an apparatus forforming the damping means of the present invention on a spindle; v

FIG. 4 is a longitudinal sectional view of a portion of the spindle andone of thefixtures for supporting the spindle during formation of thedamping means on the spindle and taken along line 4-4 of FIG. 3;

FIG. 5 is a cross sectional view of the fixture of FIG. 4 and takenalong line 5-5 of FIG. 3; and

FIG. 6 is a cross sectional view of the other of the fixtures forsupporting the spindle during formation of the damping means on thespindle and taken along line 6-6 of FIG. 3.

Referring to the drawings and particularly FIG. 1, there is shown acenterless grinding machine having a base 10 on which is supported agrinding wheel 11 for rotation about an axis, which is fixed withrespect to the base 10. A workpiece 12, which is to be ground by thegrinding wheel 11, is supported on a work rest blade 14.

The workpiece 12 is pressed against the grinding wheel 11 by aregulating wheel 15. The regulating wheel 15 rotates at a reduced speedand serves to re gulate or control the rotation of the workpiece 12 asit is being ground by the grinding wheel 1 1.

The regulating wheel 15 is carried by a wheelhead 16, which is guided byways 17 on a lower slide 18. The

lower slide 18 is slidably guided for sliding movement on the base andcarries the work rest blade 14 at its forward end.

A clamp 19 secures the wheelhead 16 to the lower slide 18 so that thetwo will move together as a unit on the base 10. A second clamp 20secures the lower slide 18 to the base 10 whereupon the wheelhead 16 maybe traversed along the lower slide 18 by releasing the clamp 19.

The structure of the foregoing centerless grinding machine is moreparticularly shown and described in U.S. Pat. No. 2,889,665 to Jessup,et al. The details of the operation of the centerless grinding machineare jdescribed in the aforesaid J essup, et al. patent.

The grinding wheel 11 is supported on one end of a spindle 21, which isrotatably supported within the base 10 by bearings 22 and 23 such asshoe bearings, for example, in the manner more particularly shown anddescribed in U.S. Pat. No. 2,507,558 to Dall, et al. The

bearings 22 and 23 support longitudinally spaced portions of the spindle21.

As shown in FIG. 2, the grinding wheel 11 utilizes balls 24 to balancethe grinding wheel v1 1. The dynamic balance mechanism, which utilizesthe balls 24, is more particularly shown and described in the aforesaidDall, et al. patent. While the balls 24 balance the grinding wheel 11,there is still a vibration produced in the spindle 21 because of bendingof the spindle 21 due to the engagement of the grinding wheel 11 withthe workpiece 12. This engagement creates a displacement of the grindingwheel 11 that'is transmitted to the spindle 21 whereby the spindle 21vibrates.

To increase the minimum dynamic stiffness of the spindle 21 whereby theamplitude of its vibration can be reduced so that regenerative chatteris eliminated, the spindle 21 has a sleeve 25 of a viscoelastic materialbonded thereto for a substantial portion of its length between thebearings 22 and 23. The sleeve 25 of the viscoelastic material, whichmay be polyvinyl chloride, for example, is disposed in surroundingrelation to the spindle 21 to absorb the vibrations of the spindle 21.The sleeve 25 absorbs the vibrations due to compression, tension, andshear strains created inthe viscoelastic material by the vibrations ofthe spindle 21. The length of the sleeve 25 is as long as possible tosurround as much of the length of the spindle 21 between the bearings 22and 23 as possible to increase the absorption of vibrations of thespindle 21 by the viscoelastic material. As the length of the sleeve 25is increased, the dynamic stiffness of the spindle 21 increases wherebythe amplitude of vibration of the spindle 21 is decreased.

The sleeve 25 of viscoelastic material has a sleeve 26, which ispreferably formed of metal but may be formed of any suitable material,including a plastic, that will constrain the sleeve 25 when the spindle21 vibrates, in surrounding relation thereto and bonded thereto. Thesleeve 26 is employed to constrain the sleeve 25 so as to increase theshear strains in the viscoelastic material of the sleeve 25 whereby thedamping, which is produced by the sleeve 25 of viscoelastic material, isincreased. This allows the viscoelastic material to absorb more energyto increase the minimum dynamic stiffness of the spindle 21.

Referring to FIGS. 3 to 6, there is shown an apparatus for fonning thesleeve 25 of viscoelastic material between the spindle 21 and theconstraining sleeve 26. The apparatus includes fixtures 27 and 28disposed in surrounding relation to the spindle 21 and the sleeve 26.

The sleeve 26 has its lower end supported in the lowerv fixture 28,which comprises a pair of semicircular members 29 and 30 (see FIG. 6)secured to each other by bolts 31. The sleeve 26 rests on bottom surface32 of a recess 33, which is formed in both the members 29 and 30 of thelower fixture 28. By disposing the sleeve 26 within the recess 33, thesleeve 26 is spaced from the spindle 21 a uniform distance. g Y

The upper fixture 27 includes a pair of semicircular upper members 34and 35 (see FlG.. 5), which are secured to each other by bolts 36, and alower annular member 37, which is supported by the upper end of thesleeve 26. The member 37 supports the members 34 and 35 by having areduced upper annular portion 38 (see FIG. 4) receiving the lower endsof the members 34 and 35.

The upper members 34 and 35 of the fixture 27 have passages 39 and 40,respectively, extending therethrough. The passages 39 and 40 allow aliquid thermosetting resin, which forms the viscoelastic material of thesleeve 25, to be supplied to the longitudinal annular area, which hasthe same thickness throughout, between the sleeve 26'and the spindle 21to form the sleeve 25. After the resin has been supplied through thepassages 39 and 40 to the area between the sleeve 26 and the spindle 21,is cures therein to form the sleeve 25 bonded to each of the spindle 21and the sleeve 26. Suitable examples of the thermosetting material arepolyvinyl chloride and epoxies.

After the resin has cured, the fixtures 27 and 28 are removed therefrom.The semicircular members 34 and 35 of the upper fixture 27 are separatedthrough removing the bolts 36 therefrom. Then, the lower annular member37 of the upper fixture 27 is lifted overthe upper reduced end of thespindle 21. The fixture 28 is then removed through disconnecting themembers 29 and 30 from each other by withdrawing the bolts 31.

The thickness of the sleeve 25 is determined by the size of the recess33 in the lower fixture 28. Of course, the upper fixture 27 must havethe lower annular member 37 formed with a recess 41 of the same diameteras the recess 33 to insure the uniform thickness of the sleeve 25throughout its length. An increase in the thickness of the sleeve 25increases its damping capability to a predetermined thickness dependingupon the viscoelastic material of the sleeve 25.

While the present invention has shown and described the sleeve 26 assurrounding the sleeve 25, it should be understood that the minimumdynamic stiffness of the spindle 21 can be increased even if the sleeve26 is omitted. Furthermore, the sleeve 26 does not have to extend forthe length of the sleeve 25. Additionally,

neither the sleeve 25 has to completely surround the spindle 21 nor thesleeve 26 completely surround the sleeve 25 In any of the foregoingsituations, the minimum dynamic stiffness of the spindle 21 is notincreased to the same extent so that maximum effective damping is notobtained. However, any of the foregoing alterations still increases theminimum dynamic stiffness of the spindle 21 to allow an increase in thecutting stiffness without regenerative chatter occurring.

While the present invention has described the sleeve 25 of theviscoelastic material as being bonded to the spindle 21, it should beunderstood that such is not a requisite for the present invention. It isonly necessary that the sleeve 25 not slip relative to the spindle 21.Accordingly, the spindle 21 could have a non-slipping outer surface.

Likewise, it is not necessary that the sleeve 26 be bonded to the sleeve25. It is only necessary that the sleeve 26 not slip relative to thesleeve 25.

While the damping means of the present invention has been shown anddescribed as used with a grinding wheel having an automatic wheelbalancer, it should be understood that it is not necessary for thegrinding wheel to have an automatic wheel balancer. Furthermore, thepresent invention has utility in other than grinders so that it may beused with milling machines, lathes, or boring machines, for example. Theinvention has utility wherever there is bending of a spindle or rotatingshaft and it is desired to reduce the amplitude of the vibration of thespindle or the rotating shaft due to the bending; thus, it is notlimited to machine tools.

The present invention has utility with a non-rotating shaft or supportmember having a cutting element supported thereon such as a boring barof the previously mentioned boring machines. It is only necessary thatthere be vibrations in the support member or shaft for the non-tuneddamping means of the present invention to have utility.

It should be understood that it is not necessary for the support memberor shaft to have a circular cross section. Furthermore, it is not arequisite of the present invention that the cross section be constantthroughout the length of the support member or shaft; Additionally, thedamping means does not have to be disposed between bearing means for thedamping means to absorb the vibrations of a support member or shaft toincrease its minimum dynamic stiffness.-

While the viscoelastic material of the sleeve 25 has been described asbeing formed from a thermosetting resin, it should be understood thatsuch is not a requisite for satisfactory operation of the damping meansof the present invention. Thus, the viscoelastic material could be butylrubber or a silicon fluoride, for example. It would be necessary to formeither the butyl rubber or the silicon fluoride in a sheet and secure itto the shaft so that it does not slide relative thereto.

An advantage of this invention is that there is no tuning requiredbetween the shaft and the damping means. Another advantage of thisinvention is that it does not add any significant weight to the spindleor rotating shaft. A further advantage of this invention is that it doesnot affect the balance of the spindle or rotating shaft.

For purposes of exemplification, a particular embodiment of theinvention has been shown and described according to the best presentunderstanding thereof. However, it will be apparent that changes andmodifications in the arrangement and construction of the parts thereofmay be resorted to without departing from the spirit and scope of theinvention.

What is claimed is:

1. In combination:

a rotating shaft;

bearing means to support longitudinally spaced portions of said rotatingshaft;

damping means disposed between said bearing means to increase theminimum dynamic stiffness of said rotating shaft; and said damping meansincluding:

a layer of viscoelastic material of substantially uniform thicknessextending longitudinally along said rotating shaft in at least partialsurrounding relation to said rotating shaft to be movable in response tovibrations of said rotating shaft to absorb the vibrations; first meansto prevent relative sliding movement between said rotating shaft andsaid layer of viscoelasticmaterial; a member disposed in at leastpartial surrounding relation to said layer of viscoelastic material;second means to prevent relative sliding movement between said layer ofviscoelastic material and said member; and said member constraining saidlayer of viscoelastic material to increase the strains in said layer ofviscoelastic material. 2. The combination according to claim 1 in which:said first preventing means includes'bonding of said layer ofviscoelastic material to said rotating shaft;

and said second preventing means includes bonding of said member to saidlayer of viscoelastic material.

3. The combination according to claim 2 in which:

said layer of viscoelastic material comprises a sleeve disposed insurrounding relation to said rotating shaft;

and said member comprises a second sleeve disposed in surroundingrelation to said sleeve of viscoelastic material, said second sleeveconstraining said sleeve of viscoelastic material to increase thestrains in said sleeve of viscoelastic material.

4. The combination according to claim 3 in which said second sleeveextends for the length of said sleeve of viscoelastic material.

5. The combination according to claim 2 in which said layer ofviscoelastic material surrounds said rotating shaft.

6. The combination according to claim 5 in which said member extends forthe length of said layer of viscoelastic material.

7. The combination according to claim 2 in which said member extendsforthe length of said layer of viscoelastic material.

8. The combination according to claim 1 in which: said layer ofviscoelastic materialcomprises a sleeve disposed in surrounding relationto said rotating shaft; and said member comprises a second sleevedisposed in surrounding relation to said sleeve of viscoelasticmaterial, said second sleeve constraining said sleeve of viscoelasticmaterial to increase the strains in said sleeve of viscoelasticmaterial. v

v9. The combination according to claim 8 in which said second sleeveextends for the length of said sleeve of viscoelastic material. r

10. The combination according to claim 1 in which said layer ofviscoelastic material surrounds said rotating shaft.

11. The combination according to claim 10 in which said member extendsfor the length of said layer of viscoelastic material.

12. The combination according to claim 1 in which said member extendsfor the length of said layer of viscoelastic material.

1. In combination: a rotating shaft; bearing means to support longitudinally spaced portions of said rotating shaft; damping means disposed between said bearing means to increase the minimum dynamic stiffness of said rotating shaft; and said damping means including: a layer of viscoelastic material of substantially uniform thickness extending longitudinally along said rotating shaft in at least partial surrounding relation to said rotating shaft to be movable in response to vibrations of said rotating shaft to absorb the vibrations; first means to prevent relative sliding movement between said rotating shaft and said layer of viscoelastic material; a member disposed in at least partial surrounding relation to said layer of viscoelastic material; second means to prevent relative sliding movement between said layer of viscoelastic material and said member; and said member constraining said layer of viscoelastic material to increase the strains in said layer of viscoelastic material.
 2. The combination according to claim 1 in which: said first preventing means includes bonding of said layer of viscoelastic material to said rotating shaft; and said second preventing means includes bonding of said member to said layer of viscoelastic material.
 3. The combination according to claim 2 in which: said layer of viscoelastic material comprises a sleeve disposed in surrounding relation to said rotating shaft; and said member comprises a second sleeve disposed in surrounding relation to said sleeve of viscoelastic material, said second sleeve constraining said sleeve of viscoelastic material to increase the strains in said sleeve of viscoelastic material.
 4. The combination according to claim 3 in which said second sleeve extends for the length of said sleeve of viscoelastic material.
 5. The combination according to claim 2 in which said layer of viscoelastic material surrounds said rotating shaft.
 6. The combination according to claim 5 in which said member extends for the length of said layer of viscoelastic material.
 7. The combination according to claim 2 in which said member extends for the length of said layer of viscoelastic material.
 8. The combination according to claim 1 in which: said layer of viscoeLastic material comprises a sleeve disposed in surrounding relation to said rotating shaft; and said member comprises a second sleeve disposed in surrounding relation to said sleeve of viscoelastic material, said second sleeve constraining said sleeve of viscoelastic material to increase the strains in said sleeve of viscoelastic material.
 9. The combination according to claim 8 in which said second sleeve extends for the length of said sleeve of viscoelastic material.
 10. The combination according to claim 1 in which said layer of viscoelastic material surrounds said rotating shaft.
 11. The combination according to claim 10 in which said member extends for the length of said layer of viscoelastic material.
 12. The combination according to claim 1 in which said member extends for the length of said layer of viscoelastic material. 